Many refrigeration systems utilize a hydrofluorocarbon (HFC) refrigerant, such as R-134a (1,1,1,2-tetrafluoroethane). HFC refrigerants contain hydrogen, fluorine, and carbon and thus do not contain any ozone depleting substances, which is in contrast to chlorofluorocarbon (CFC) or hydrofluorocarbon (HCFC) refrigerants, which both contain chlorine and which have been phased out of use in refrigeration systems. However, although HFC refrigerants have an ozone depleting potential (ODP) of zero, compared to CFC and HCFC refrigerants which have ODPs as high as 1, HFCs have a high global warming potential (GWP), where GWP is the measure of how much heat a greenhouse gas traps in the atmosphere. For example, R-134 has a GWP of over 1300. For comparison, carbon dioxide is used as the control in determining GWP and has a GWP of one.
As such, many refrigerator manufacturers have contemplated using a natural refrigerant such as n-butane (R-600) or isobutane (R-600a), as these refrigerants have an ODP of zero and a GWP that is less than 10 and are also highly energy efficient. However, one drawback to the use of these natural refrigerants is that they are highly flammable and are classified as A3 refrigerants since they have a heat of combustion of greater than 19 kilojoules/kilogram. For example, butane has a heat of combustion of about 50 kilojoules/kilogram. Because these refrigerants are classified as A3 refrigerants, they are subject to a charge size limit of 57 or 150 grams in order to comply with various standards, meaning these refrigerants cannot be used in larger refrigeration systems that require more refrigerant. For comparison, if a refrigerant is classified as an A2 refrigerant having a heat of combustion of less than 19 kilojoules/kilogram, it is subject to a charge size limit of 225 grams.
Another option is to use a hydrofluoroolefin (HFO) refrigerant such as R-1234yf (2,3,3,3-tetrafluoropropene) or R-1234ze (1,3,3,3-tetrafluoropropene), which have an ODP of zero and a GWP of less than 10 and are classified as A2 refrigerants because they have a heat of combustion of around 10 kilojoules/kilogram. However, one drawback to the use of these refrigerants is that they are less energy efficient than R-134a. Further, HFO refrigerants are expensive, although R-1234ze is much less expensive than R-1234yf.
Another option is to use carbon dioxide (R-744) based refrigerants, as carbon dioxide as an ODP of zero and a GWP of 1. However, carbon dioxide refrigerants cannot be used in compressors designed for other refrigerants such as R-600, R-600a, etc. due to the higher refrigeration capacity (e.g., a different motor/displacement combination is required). Further, carbon dioxide has higher operating and standstill pressures which increases leak potential and can be hazardous. Additionally, R-744 systems require the use of steel or stainless steel pipes due to the higher operating and standstill pressures.
Accordingly, an energy efficient refrigerant having a low GWP that could be classified as an A2 refrigerant, making it suitable for use in larger refrigeration systems would be useful. A refrigerant having comparable energy efficiency to R-134a would also be useful. In addition, a refrigeration system incorporating such a refrigerant without having to change current compressor designs would also be useful.